This invention relates to an automated apparatus for performing multiplexed Capillary Electrophoresis. It is especially useful in an automated Capillary Zone Electrophoresis (CZE) system for loading samples into a plurality of capillaries from wells of commercially available, microtitre trays of standard size.
The contents of commonly-owned U.S. patent application Ser. No. 09/105,988, which issued as U.S. Pat. No. 6,027,627 and also was published as WO 99/00664 are incorporated by reference to the extent necessary to understand the present invention. This reference discloses an automated apparatus for capillary electrophoresis.
FIG. 1 illustrates a prior art automated electrophoretic apparatus discussed in the above-referenced patent application for capillary electrophoresis. The apparatus includes a light source 452, a processor/controller 404, a dual carrousel arrangement having an upper carrousel 601 and a lower carrousel 602 which are aligned and spaced apart along a common axis and operated by a rotor 604, a DC motor 605 having a movable member 603 to move a tray 214 place on one of the carrousels along a common axis toward or away from an array of capillary ends belonging to a capillary cartridge 300, a detector 408 for detecting, at a window region 130 of the capillaries, the fluorescence emitted by samples migrating along the capillaries, and a computer monitor 406 to view the results of the migration. An electrophoretic medium, such as a gel, can be introduced into the capillaries via a conduit 606 in preparation for an electrophoretic run.
FIG. 2 illustrates a prior art plumbing system in accordance with the above-identified reference, for performing capillary electrophoresis using the device of FIG. 1. In particular, FIG. 2 shows the integration of a gel syringe 8045 and an HPLC wash solvent system 807 into the solvent/gel delivery module. A solvent manifold 850 connects three inlets from the feeder tubes 806 of the solvent containers 801, 802, 803 to an outlet. Feeder tubes 806 from the solvent containers 801, 802, 803 are connected to the inlets of the solvent manifold 850 by tubing 860. The controller 404 pictured in FIG. 1 controls the solvent manifold 850 to select solvent from one of the three solvent containers 801, 802, 803. The inlet of the HPLC pump 807 is connected to the outlet of the solvent manifold 850 by tubing 861 and the outlet of the HPLC pump 807 is connected to an inlet of a valve manifold 851 by tubing 862.
The valve manifold 851 connects two inlets and an outlet. One inlet of the valve manifold 851 is connected to the gel syringe 804 by tubing 863 and the other inlet of the valve manifold 851 is connected to the outlet of the HPLC pump 807. The outlet of the valve manifold 851 is connected to the solvent/gel input port 606 by tubing 864. The controller 404 pictured in FIG. 11 causes the valve manifold 851 to select either the inlet connected to the gel syringe 804 or the inlet connected to the HPLC pump 807. In this manner, gel and solvents are delivered to the capillary cartridge 909 in preparation for capillary gel electrophoresis of samples in microtitre tray 852.
In the preferred embodiment, the tubing connecting the feeder tubes 806 of the solvent containers 801, 802, 803 to the inlets of the solvent manifold 850 is standard teflon tubing with a diameter of xe2x85x9 inches. The tubing 861 connecting the outlet of the solvent manifold 850 to the inlet of the HPLC pump 807 is PEEK tubing with a diameter of {fraction (1/16)} inches. The tubing 861 connecting the outlet of the solvent manifold 850 to the inlet of the HPLC pump 807, the tubing 862 connecting the outlet of the HPLC pump 807 to an inlet of the valve manifold 851, the tubing 863 connecting the gel syringe 804 to an inlet of the valve manifold 851 and the tubing 864 connecting the outlet of the valve manifold 851 to the solvent/gel input port are PEEK tubing with a diameter of {fraction (1/16)} inches.
FIG. 3 illustrates a preferred embodiment of capillary cartridge 1180 in accordance with the above-identified application. In this embodiment, the capillary tubes run from their first ends 1188 disposed in an electrode/capillary array 1181. The capillary tubes then run inside multilumen tubing 1183. The multilumen tubing is taught in detail in U.S. patent application Ser. No. 08/866,308, which is incorporated by reference herein. The multilumen tubing 1183 is held firmly in place by tubing holders 1185. The capillary tubes, without the protection the multilumen tubing, pass through an optical detection region 1187. Beyond the optical detection region 1187, the capillary tubes have a common termination and are bundled together and cemented into a high pressure T-shaped fitting 1182 made from electrically conductive material, which, during electrophoresis, is connected to electrical ground.
The tubing holders 1185 and the T-fitting 1182 are fixed to a cartridge base 1186. The cartridge base 1186 is made from polycarbonate plastic for its dielectric characteristic. The base 1186 in turn is removably attached to a shuttle 1179 which includes a set of rail couplings 1184 protruding from its bottom. These rail couplings 1184 are arranged so that they fit on to a railing system (not shown in FIG. 18) of the apparatus in FIG. 1. The railing system allows the shuttle 1184 to move between an in position and out position. The base 1186 is detached from the shuttle 1179 so that the cartridge 1180 is disposed (or cleaned) and a new (or cleaned) capillary cartridge is attached when the shuttle 1179 is in its out position. The combination of the railing system and the shuttle 1179 allows the newly attached capillary cartridge to be repeatedly located at the same position as that of the disposed capillary cartridge in relation to a camera and a laser (not shown in FIG. 3) when the shuttle 1179 is in its in position. In a preferred embodiment, the shuttle 1179 extends the length of the base 1186 with an opening to accommodate the electrode/capillary array 1181; the shuttle 1179 is attached to the base 1186 by a plurality of removable fasteners 1178.
The prior art plumbing system of FIG. 2 and T-fitting of FIG. 3 are best suited for capillary gel electrophoresis. In capillary gel electrophoresis, the gel is fairly viscous, on the order of 50,000 centi-poise. This requires a system which can create pressure sufficient to load gel into the capillaries in preparation for a capillary electrophoresis run, and sufficient to expel the gel from the capillaries during reconditioning.
In contrast to the gels that are used in capillary gel electrophoresis, buffers are used to load the capillaries in capillary zone electrophoresis (CZE). These buffers have a viscosity on the order of that of water, i.e., about 1 centi-poise. While the low viscosity of buffers has the advantage of not needing high pressure to load and unload the electrophoretic medium, CZE with buffers does have the disadvantage of capillary siphoning. Capillary siphoning is characterized by the buffer solution at one end of the capillaries being completely drawn into the capillaries, thereby depleting the buffer at that one end. Like siphoning of any tubing, this problem occurs when the two ends of the capillaries terminate at different heights. The obvious solution to this problem is to ensure that opposite ends of the capillaries are maintained at the same level. This, however, is less than an ideal solution.
The present invention is directed to an automated parallel capillary zone electrophoresis (CZE) system. The CZE system of the present invention is realized by modifying the prior art capillary gel electrophoresis (CGE) system of the above-reference prior art. More particularly, the present invention is principally realized by modifying the plumbing at the ends of the capillaries towards which samples in the capillaries migrate.